This invention relates to the identification of objects which have been encoded and more particularly to the identification of objects using radar techniques in which the object being examined moves relative to the radar source and is passively or actively encoded.
In many instances it is desirable to identify a particular object. Typical examples are in the fields of transportation, manufacturing, inventory control, postal sorting, etc. In these fields it often happens that the objects are of like kind and are either indistinguishable, too numerous or separated in distance to be rapidly identified using conventional means. Therefore, a suitable label such as an encoding array, must be provided to accomplish their rapid identification. The encoding array permits the object being examined by a reader (radar) to be identified using conventional radar techniques.
Examples of encoding array labels presently in use are based on electromagnetic principles for their operation. In each case readers are used to detect and decode the information in the label. In each of these types of devices, including both the label and the reader, the main criteria which determine their effectiveness are physical size, weight, power consumption, cost, etc., contrast and resolution. The physical size of the label, for example, determines to a great extent the physical size, weight, power consumption, and cost etc., of the reader. Since the label must be smaller than the object to which it is attached, the reader must be compatible to insure readibility, efficiency, and economy of its use. Contrast is a term which denotes the ability of the reader to detect the label and determine its code in the general presence of influences or reflections from the object itself. The term resolution is most frequently used to denote the smallest extension within the encoded array label which the reader is able to separate or differentiate.
Two examples of labeling systems presently in use are based on simple radars used to read the polarization or resonant frequency of elements in the label and, as disclosed in my copending application, using coherent synthetic aperture radar to read the label elements. In a system using simple radar the reader size, weight, power consumption, cost, etc., the contrast and resolution are severely limited by the range between the label and reader, and by the wavelength and aperture size employed by the reader. The simple radar system, therefore, has the potential to achieve fine range resolution but appears to be constrained to relatively poor azimuthal or angular resolution especially at long operating ranges. As I have pointed out in my copending application, a coherent radar which utilizes the principle of synthetic aperture is not burdened by the parameters of wavelength, range, and aperture dimension and can operate at any frequency, practical range, thus providing capabilities over simple radars.